Material level indicator

Abstract

A system for indicating level of material in a vessel comprising a probe which includes a plurality of electrically discrete probe elements of electrically conductive construction position within a material vessel in a spaced array extending height-wise of the vessel. Each probe element has electrical characteristics which vary as a function of proximity of material thereto within the vessel. In one embodiment, the probe elements comprise capacitive elements responsive to varying dielectric characteristics as material approaches each element. In another embodiment, having particularly utility in fuel level sensing applications, the probe elements comprise resistance elements responsive to cooling through immersion in fuel for varying voltage drop thereacross. Electonic circuitry is coupled to the several probe elements for detecting material level as a function of electrical characteristics of the probe elements. Preferably, such level detection is accomplished in discrete steps corresponding to separation between probe elements.

The invention claimed is: 
     
       1. A system for indicating level of material in a vessel comprising: resistance probe means including a plurality of electrically discrete resistor probes of electrically conductive construction positioned within the vessel in a spaced array extending height-wise of the vessel, said probes being characterized by having electrical resistances which vary as a function of heat dissipative coupling with material in the vessel,   said resistance probe means comprising a continuous layer of resistance material on a planar rectangular substrate, said resistance layer being of serpentine contour height-wise of the vessel, and first and second opposed electrical contact means positioned in alternate undulations of said resistive layer height-wise of the vessel, said resistance layer and said contact means being carried on one face of said substrate,   said first contact means comprising a first array of contacts extending from one edge of said substrate and being interconnected by an electrical bus which extends along said edge, said second contact means comprising discrete second contacts extending from an opposing edge of said substrate,   first circuit means individually connected to said discrete probes and being responsive to variation of said electrical characteristics, and   second circuit means coupled to said first circuit means and responsive to total variation of said electrical characteristics collectively at said probes for indicating level of material in the vessel adjacent to said probes.   
     
     
       2. The system set forth in claim 1 wherein each adjacent pair of said first contacts and that portion of said bus extending therebetween substantially encloses an opposing one of said second contacts. 
     
     
       3. A system for indicating level of material in a vessel comprising: a probe which includes a continuous strip of electrical resistance material on a substrate and extending height-wise of the vessel, and first and second arrays of electrical contacts disposed along opposite sides of said strip on said substrate, contacts of said first and second arrays being electrically alternately connected to said strip height-wise of the vessel,   first circuit means including means connecting all contacts of said first array to a source of electrical power, means individually coupled to contacts of said second array and responsive to electrical resistance characteristics of individual sections of said strip between said alternately-connected contacts of said first and second arrays as a function of heat dissipative coupling of said strip sections to material in the vessel, and   second circuit means coupled to said first circuit means and responsive to total variation of said resistance characteristics of said strip section connected in parallel to said first circuit means for indicating level of material in the vessel adjacent to said probe.   
     
     
       4. The system set forth in claim 3 wherein said second circuit means comprises threshold detection means individually responsive to said strip sections for providing digital output signals as a function of proximity of material in the vessel to individual said probe, and means for indicating material level in discrete steps as a function of said digital signals. 
     
     
       5. The system set forth in claim 4 wherein said second circuit means comprises a resistor summing network including a plurality of first resistors each having a firs terminal coupled to the output of an associated said threshold detection means and a second terminal connected to a common junction, and display means connected between said common junction and a source of electrical power. 
     
     
       6. The system set forth in claim 3 wherein said strip is of serpentine contour heightwise of the vessel, said contacts of said first and second arrays being disposed in alternate undulations of said strip. 
     
     
       7. The system set forth in claim 6 wherein said substrate is of planar rectangular construction, said strip and said contact arrays being carried on one face of said substrate. 
     
     
       8. The system set forth in claim 7 wherein said contacts of said first array extend from one edge of said substrate and are interconnected by an electrical bus which extends along said one edge, and wherein said contacts of said second array extend from an opposing edge of said substrate.